From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-x242.google.com (mail-qk0-x242.google.com [IPv6:2607:f8b0:400d:c09::242]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 40mYJP3n81zF14g for ; Thu, 17 May 2018 11:15:14 +1000 (AEST) Received: by mail-qk0-x242.google.com with SMTP id s70-v6so2318829qks.13 for ; Wed, 16 May 2018 18:15:14 -0700 (PDT) Date: Thu, 17 May 2018 09:19:49 +0800 From: Boqun Feng To: Mathieu Desnoyers Cc: Peter Zijlstra , "Paul E. McKenney" , Andy Lutomirski , Dave Watson , linux-kernel , linux-api , Paul Turner , Andrew Morton , Russell King , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andrew Hunter , Andi Kleen , Chris Lameter , Ben Maurer , rostedt , Josh Triplett , Linus Torvalds , Catalin Marinas , Will Deacon , Michael Kerrisk , Joel Fernandes , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , linuxppc-dev Subject: Re: [PATCH 07/14] powerpc: Add support for restartable sequences Message-ID: <20180517011949.GA1121@tardis> References: <20180430224433.17407-1-mathieu.desnoyers@efficios.com> <20180430224433.17407-8-mathieu.desnoyers@efficios.com> <20180516161837.GI12198@hirez.programming.kicks-ass.net> <112970629.1913.1526501596485.JavaMail.zimbra@efficios.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="qMm9M+Fa2AknHoGS" In-Reply-To: <112970629.1913.1526501596485.JavaMail.zimbra@efficios.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , --qMm9M+Fa2AknHoGS Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, May 16, 2018 at 04:13:16PM -0400, Mathieu Desnoyers wrote: > ----- On May 16, 2018, at 12:18 PM, Peter Zijlstra peterz@infradead.org w= rote: >=20 > > On Mon, Apr 30, 2018 at 06:44:26PM -0400, Mathieu Desnoyers wrote: > >> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig > >> index c32a181a7cbb..ed21a777e8c6 100644 > >> --- a/arch/powerpc/Kconfig > >> +++ b/arch/powerpc/Kconfig > >> @@ -223,6 +223,7 @@ config PPC > >> select HAVE_SYSCALL_TRACEPOINTS > >> select HAVE_VIRT_CPU_ACCOUNTING > >> select HAVE_IRQ_TIME_ACCOUNTING > >> + select HAVE_RSEQ > >> select IRQ_DOMAIN > >> select IRQ_FORCED_THREADING > >> select MODULES_USE_ELF_RELA > >> diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal= =2Ec > >> index 61db86ecd318..d3bb3aaaf5ac 100644 > >> --- a/arch/powerpc/kernel/signal.c > >> +++ b/arch/powerpc/kernel/signal.c > >> @@ -133,6 +133,8 @@ static void do_signal(struct task_struct *tsk) > >> /* Re-enable the breakpoints for the signal stack */ > >> thread_change_pc(tsk, tsk->thread.regs); > >> =20 > >> + rseq_signal_deliver(tsk->thread.regs); > >> + > >> if (is32) { > >> if (ksig.ka.sa.sa_flags & SA_SIGINFO) > >> ret =3D handle_rt_signal32(&ksig, oldset, tsk); > >> @@ -164,6 +166,7 @@ void do_notify_resume(struct pt_regs *regs, unsign= ed long > >> thread_info_flags) > >> if (thread_info_flags & _TIF_NOTIFY_RESUME) { > >> clear_thread_flag(TIF_NOTIFY_RESUME); > >> tracehook_notify_resume(regs); > >> + rseq_handle_notify_resume(regs); > >> } > >> =20 > >> user_enter(); > >=20 > > Again no rseq_syscall(). >=20 > Same question for PowerPC as for ARM: >=20 > Considering that rseq_syscall is implemented as follows: >=20 > +void rseq_syscall(struct pt_regs *regs) > +{ > + unsigned long ip =3D instruction_pointer(regs); > + struct task_struct *t =3D current; > + struct rseq_cs rseq_cs; > + > + if (!t->rseq) > + return; > + if (!access_ok(VERIFY_READ, t->rseq, sizeof(*t->rseq)) || > + rseq_get_rseq_cs(t, &rseq_cs) || in_rseq_cs(ip, &rseq_cs)) > + force_sig(SIGSEGV, t); > +} >=20 > and that x86 calls it from syscall_return_slowpath() (which AFAIU is > now used in the fast-path since KPTI), I wonder where we should call So we actually detect this after the syscall takes effect, right? I wonder whether this could be problematic, because "disallowing syscall" in rseq areas may means the syscall won't take effect to some people, I guess? > this on PowerPC ? I was under the impression that PowerPC return to > userspace fast-path was not calling C code unless work flags were set, > but I might be wrong. >=20 I think you're right. So we have to introduce callsite to rseq_syscall() in syscall path, something like: diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S index 51695608c68b..a25734a96640 100644 --- a/arch/powerpc/kernel/entry_64.S +++ b/arch/powerpc/kernel/entry_64.S @@ -222,6 +222,9 @@ system_call_exit: mtmsrd r11,1 #endif /* CONFIG_PPC_BOOK3E */ =20 + addi r3,r1,STACK_FRAME_OVERHEAD + bl rseq_syscall + ld r9,TI_FLAGS(r12) li r11,-MAX_ERRNO andi. r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TI= F_PERSYSCALL_MASK) But I think it's important for us to first decide where (before or after the syscall) we do the detection. Regards, Boqun > Thoughts ? >=20 > Thanks! >=20 > Mathieu >=20 > --=20 > Mathieu Desnoyers > EfficiOS Inc. > http://www.efficios.com --qMm9M+Fa2AknHoGS Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAABCAAdFiEEj5IosQTPz8XU1wRHSXnow7UH+rgFAlr82LEACgkQSXnow7UH +rigrAf9F+civFS4yvkbV5+5YY7LO3c7DJGBFUVnW4gUwQ14uGxh/pzKh9n2Sz1A RUVz++oMugIjA3y4/4dLCEjaG8D1qZ96dTJ01vHakA+ieg6rJ0a2/hqrH2lDur9/ HDrrniFt823LtzZrZtg6gAimOXsRS/lAMJftmrbwDgzNjenr4iOOklZRx/vX7W7k nE/w1BChYNKSqbv8LIGpFLbOdDl1rstDhdAfyq0STjsw15LiL389Ae07MVbibt89 xC06lV+o7EnibHXg7p2K/EJzEG8PYmNRmanayu8Rtw2fwKULbUFiuNJB5L5l27Q+ SdKzROnL22KVhC+kPzLx7l/yI0386Q== =nkk3 -----END PGP SIGNATURE----- --qMm9M+Fa2AknHoGS--